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August 2006

August 2006. Vectorless ICT - Best Practice Techniques With FrameScan FX. Audio Dial-In US/Canada:  877-809-3723 Int'l/Local: +1.706.634.0863 ID: 4244988 or Teradyne. Tony Suto anthony.suto@teradyne.com. Web Seminar Goals. To better understand:

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August 2006

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  1. August 2006 Vectorless ICT - Best Practice Techniques With FrameScan FX Audio Dial-In US/Canada:  877-809-3723 Int'l/Local: +1.706.634.0863 ID: 4244988 or Teradyne Tony Suto anthony.suto@teradyne.com

  2. Web Seminar Goals • To better understand: • How the basic hardware technology operates • How the software algorithms operate on the data • What the tradeoffs are with the technology • The limits of use of the technology

  3. What is FrameScan FX? • Teradyne FrameScan FX is the latest vectorless in-circuit test technique to identify open pins on IC devices and connectors • Reliably tests the latest small packaged IC devices • FS-FX was the first to use intelligent program algorithms to optimize test time and measurement stability on a per pin basis • High device pin coverage • Fast test execution • Rapid program development, no digital vectors needed • Compatible with existing FrameScan hardware, simply replace active probe component

  4. Gain Filter Opens Sensor Scanner MuxBoard Device- Under-Test Low Noise ActiveBufferAssembly ProbePlate Sensor DUT ICLead Printed Circuit Board Guard AC Source DSP Based AC Detector ICA FrameScan FX Hardware Components

  5. Capacitance to Voltage Relationship Rf Discrete Fourier Transform Xc = 1 / (2*Pi*f*C) Gain K2 A/D Cx Vs Gain K1 AC Source Vmeas = Vsx K1x K2 K1 = Rfx 2 xpx Ftx Cx Vmeas = Vsx( Rfx 2 xpx Ftx Cxx K2 ) Cx = Vmeas / (Vsx Rfx 2 xpx Ftx K2 ) Where: Vmeas = The measured pin voltage (Vpeak) Vs = The stimulus voltage (Vpeak) K1 = The active probe voltage gain @the test frequency (V/V) K2 = All additional path gain @ the test frequency (V/V) Rf = The value of the feedback resistance (Ohms) Ft = The test frequency (Hz) Cx = The probe coupling capacitance (Farads) Vmeas Vmeas Gain Term

  6. FrameScan FX Resolution Limits: Rf = 20 Meg Discrete Fourier Transform Xc = 1 / (2*Pi*f*C) Gain K2 = 27V/V A/D Cx = 0.2fF Gain K1 Vs = 0.4Vpeak Ft = 9.5Khz 5mV limit Vmeas Teradyne has determined that the lowest reliable measurement voltage is 5mV Filling in the equation on the last slide we have: Cx = 5E-3/ (0.4x 20E6 x 2 xpx 9.5kHz x 27) = 3.88E-16pF Therefore 5mV equates to 0.4fF Conclusion: Framescan FX measures as low as 0.4fF

  7. Why Guarding is Important Equivalent Circuit ActiveBuffer Ia Ca Opens Sensor plate Node A ActiveBuffer Rx Cb BGA Under-Test Ca Cb AC Source Ib Node B Guard Node B Rx Printed Circuit Board Node A All nodes not being tested need to be guarded, otherwise other pin paths will add to the measured signal AC Source Guard

  8. FrameScan FX and Floating Metal BGAs Equivalent Circuit ActiveBuffer Cc-m Cm-p Opens Sensor plate Floating Metal Top Metal BGA Under-Test ActiveBuffer Printed Circuit Board BGA with floating metal tops/heat spreaders are testable! AC Source Guard Guards

  9. FrameScan FX and Grounded Metal BGAs Equivalent Circuit ActiveBuffer Cc-m Cm-p Opens Sensor plate Grounded Metal Top Metal BGA Under-Test ActiveBuffer Rx Rx Printed Circuit Board Guarding grounded BGA ground signal results in loss of coverage AC Source Guard Guards

  10. FrameScan FX and Grounded Metal BGAs Equivalent Circuit ActiveBuffer Cc-m Cm-p Opens Sensor plate Grounded Metal Top Metal BGA Under-Test ActiveBuffer Rx Zn Rx To receive a signal, the guard needs to be removed, but this results in multiple error paths and false passes Printed Circuit Board AC Source Guard Open Guards

  11. PCIExpress x4 Connector Top View 4 1 3 5 6 7 8 9 10 11 2 15 12 13 14 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Row A Row B 9 1 2 3 4 5 6 7 8 10 11 12 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 31 13 30 32 Ground Signal Differential Pair Power Testing Power Grounds on Connectors • PCI Express has 21 grounds • To find a single open pin requires setting a threshold that is ½ of a pins contribution to the overall measured signal • This is 1/42, or 2.4% of the total measured signal • Measurement repeatability needs to be far less than +/-2.4% Threshold required to find one open pin Total Measured signal Individual pin contributions

  12. Testing Power Grounds on Connectors • Assume that each pin contributes 10mV, so the total connector will measure 21*10mV, or 210mV • The threshold to find a single open pin needs to be set to ½ a pin contribution, or 210mV - 5mV= 205mV • This threshold needs to be set at least 3.6 sigma away from the average measurement to minimize false calls (This is for a CPK=1.2). • 3.6*Sigma = 5mV, Sigma = 1.38mV • SNR required for reliable measurement will be: SNR = 20 log [210/ 1.38], or SNR > 44dBV • All other sources of measurement variability (probe landing, board to board variations etc) need to create far less than a 1.38mV delta for reliable tests • Achieving less than 0.66% total measurement variation in a production environment is next to impossible! 205mV Threshold 210mV 10mV

  13. Test Frequency and Amplitude • Teradyne FrameScan FX uses 9.5 kHz sinewave test signal at 0.4V peak • Why 9.5 kHz ? • A higher frequency will result in a larger measurement signal, BUT also creates additional parasitic signal coupling on the board yielding less reliable results. • Operating at a lower frequency generates smaller signals and therefore has no net benefit. • Teradyne found that signals between 8 kHz and 12 kHz work the best for FS FX • Why 0.4V peak? • Smaller test signals will result in smaller measurements and lower measurements will cause a decrease in fault coverage. • Larger voltages can begin to turn on ESD and other PN junctions on the connected IC devices resulting in other parasitic signal paths. Increasing the amplitude will result in increased false pass measurements on open pins • Increasing the voltage can also potentially damage low voltage devices

  14. FrameScan FX Source Loading • On certain IC pins, there may be a large capacitor which will load down the source signal (Low threshold = 100mV) • FS FX algorithm automatically detects source loading and: • Automatically switches to one of two lower frequencies to eliminate source loading and increase pin coverage IC Xc = 1 / (2*Pi*f*C) C = 10 uF Ft1 = 9.5kHz Ft2 = 166.7Hz Ft3 = 16.7Hz Board under test ICA

  15. Precision-Mode Algorithm Overview Max = 30mV • Measured pin values are compared against thresholds that are determined from known good board measurements • During the learn process, algorithm measures each pin signal ten times to determine signal amplitude and stability • Amplitude must be: > 5mV • For stable measurements: Avg = 20mV Min = 15mV 5mV Threshold (Max-Min) / (Avg) < 0.2 (30-5) / 20 = 1.25, so unstable U16, pin 24

  16. Precision Mode Algorithm Overview • If pin stability is inadequate, algorithm automatically re-tests the pin in a high-precision mode, increasing SNR by another 6dBV • If low measuring pin now passes, it will then be automatically tested in precision mode during production Max = 29mV Avg =27mV Min = 25mV 5mV Threshold (Max-Min) / (Avg) < 0.2 (29-25) / 27 = 0.15, so pin 24 is now stable in precision mode U16, pin 24

  17. Digital Signal Processing and Noise • The amount of noise in the measurement is a function of the bandwidth of the system. • Minimizing the bandwidth reduces the noise and improves the measurement repeatability • Vnoise = V/SQRT(Hz) * SQRT (Bandwidth in Hz) • DFT bandwidth = Fs/N ~ 1/Time • Where: Fs = Digitizer samples per second N = Digitizer number of samples • So taking more time, improves stability

  18. Gaussian or “normal” distribution for the FX voltage measurements X • SNR = 20 LOG [ (X- σ) / σ ] Where: • SNR = signal to noise ratio • X = Mean msmt. value • σ= Std dev =. Vnoiserms 20dBV = 10:1 40dBV = 100:1 60dBV = 1000:1 σ FrameScan FX Signal to Noise Ratio • When noise is a random and uncorrelated process relative to the measurement sampling rate, the standard deviation ( σ ) of the voltage measurements is equal to the RMS voltage of the noise. SNR can be calculated using the mean measurement value ( X )and σ:

  19. Intelligent Threshold Setting Algorithm • Patented Technology for setting pin pass/fail thresholds US Patent # 5391993 • Dynamically determines thresholds values on a per pin basis • Automatically weighs adjacent pin measured values for setting each pin threshold value • Algorithm accommodates systemic shifts in all measured pin values (physical probe contact changes, etc) • Pin thresholds can be averaged across multiple boards • Accommodates multiple pin connections on signal

  20. Gain Filter Opens Sensor Scanner MuxBoard Device- Under-Test ActiveBufferassembly ProbePlate DUT ICLead Printed Circuit Board Guard AC Source AC Detector ICA Framescan FX Algorithm Summary • FrameScan FX sampling options for optimizing tests • AUTO mode • Two sampling passes made, first in high speed mode, then precision mode for low measurement value pins for high accuracy 6dBV, or 2:1 improvement of the signal to noise ratio (SNR) (Intelligent test) • HIGH mode • All pin data is collected in high precision mode in a single pass with a typical SNR improvement of 6dBV • STANDARD mode • All pin data is collected in high speed mode in a single pass

  21. FrameScan FX Summary • Teradyne FrameScan FX is the latest vectorless in-circuit test technique to identify open pins on IC devices and connectors • The first to use intelligent program algorithms optimize test time and measurement stability on a per pin basis • Reliably measures capacitance coupling to 0.4fF for testing the smallest of packages for open pins • Uses smart algorithms to estimate the percentage of board coupling to more accurately set pin thresholds, so no false passes on open pins • Employs source loading detection and automatically switches to one of two lower frequencies to eliminate loading and gain pin coverage • Optimized to test small package type devices on PCBs

  22. Teradyne Assembly Test Division Website: www.teradyne.com/atd

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